Re: Question re: SSA Aggressive Dead Code Elimination

[Diego Novillo <dnovillo at redhat dot com>]

On Wed, 27 Jun 2001, Daniel Berlin wrote:

> law@redhat.com writes:
> 
> > I'm not sure which is the better solution.  
> 
> Oh, and BTW, the reason you are running into this problem is that
> you've changed the dominance frontier (by removing 0 as a dominator of
> 1) , and thus, changed the IDF, and thus, eliminated the need for a
>    phi node there. 
> I think, anyway.
>
No.  The dominance frontier was never changed.  What changed was
that the phi term stopped being important because we deleted one
of its arguments.

> To quote another paper abstract to make sure muchnik's not just wrong,
> "
>                  In this paper, we present an almost-linear time
>                  algorithm for constructing Gated Single Assignment
>                  (GSA), which is SSA augmented with gating functions at
>                  {$\phi$}-nodes. The gating functions specify the
>                  control dependences for each reaching definition at a
>                  {$\phi$}-node. 
> "
> Which is what we've got, no?
> 
Nope.  What we ended up having was a trivially dead phi term.


Diego.